Where does the solar system end?

Depending on how it is defined, the boundary of the Solar System can be the Kuiper Belt, the heliopause, or the Oort Cloud.

The Solar System consists of 8 planets. Photo: NASA/JPL — The Solar System consists of 8 planets. Photo: *NASA/JPL*

The Solar System is huge, containing eight planets, five dwarf planets, hundreds of moons, and millions of asteroids and comets. They all orbit the Sun, and in many cases each other, at speeds of thousands of kilometers per hour. So where does the Solar System end? The answer depends on how you define the planetary system.

According to NASA, the Solar System has three potential frontiers: the Kuiper Belt (a belt of rocky bodies beyond Neptune's orbit), the heliosheath (the edge of the Sun's magnetic field), and the Oort Cloud (a distant comet-containing region that is nearly invisible from Earth).

Kuiper Belt

The Kuiper Belt extends from 30 to 50 astronomical units (AU) from the Sun (1 AU is the distance between Earth and the Sun). This region is filled with asteroids and dwarf planets, such as Pluto, that have been ejected from the inner solar system by gravitational battles with the planets.

Some astronomers argue that the Kuiper Belt should be considered the edge of the Solar System because it represents what would have been the edge of the Sun's protoplanetary disk. The protoplanetary disk is a belt of gas and dust that later evolved into planets, moons, and asteroids.

"If we narrowly define the solar system as just the Sun and the planets, then the edge of the Kuiper Belt can be considered the edge of the solar system," said Dan Reisenfeld, a researcher at the Los Alamos National Laboratory in New Mexico, USA.

The Kuiper Belt is full of asteroids surrounding the Solar System. Photo: BBC — The Kuiper Belt is full of asteroids surrounding the Solar System. Photo: *BBC*

But some astronomers consider this definition too simplistic. “It’s not really true. Things have moved a lot – mostly outwards – since the planets formed,” explains Mike Brown at the California Institute of Technology (Caltech).

Accordingly, the Kuiper Belt does not contain everything in the Solar System. In October 2023, the discovery of a series of new objects outside the Kuiper Belt suggested that there may be a "second Kuiper Belt" further out. Some researchers believe that the uncertainty about the outer edge of this region makes it impossible to be a reliable boundary of the Solar System.

Japan full

The heliopause is the outer edge of the heliosphere — the region affected by the Sun’s magnetic field. At heliopause, the solar wind, or stream of charged particles emitted by the Sun, becomes too weak to repel the incoming radiation from other stars and cosmic entities in the Milky Way.

"Because the plasma inside the heliosheath originates from the Sun and the plasma outside the heliosheath originates from the interstellar region, some people consider the heliosheath to be the boundary of the solar system," Reisenfeld said. The space outside the heliosheath is also often called "interstellar space" (the space between stars).

Two spacecraft have crossed the heliopause: Voyager 1 in 2012 and Voyager 2 in 2018. As they flew beyond the heliopause, the Voyagers quickly detected changes in the type and level of magnetism and radiation coming toward them. This suggests they crossed some kind of boundary, Brown said.

However, the heliosphere is not spherical but rather an elongated mass. Therefore, using the heliopause to define the Solar System would create a distorted system, which goes against the views of some researchers on planetary systems.

Simulation of Voyager 1 and Voyager 2 flying in space. Photo: NASA/JPL-Caltech — Simulation of Voyager 1 and Voyager 2 flying in space. Photo: *NASA/JPL-Caltech*

Oort Cloud

According to NASA, the Oort Cloud is the farthest and widest potential boundary of the solar system, stretching out to about 100,000 AU from the star. "People who define the solar system as everything gravitationally bound to the sun consider the edge of the Oort Cloud to be the edge of the solar system," Reisenfeld said.

For some researchers, this is an ideal choice for the boundary of the Solar System because, in theory, a planetary system consists of all objects orbiting a star. However, other researchers argue that the Oort Cloud is located in interstellar space and therefore outside the Solar System, even if it is bound to the Sun. In addition, scientists are uncertain about where the Oort Cloud actually ends, making it a less reliable boundary than the Kuiper Belt.

Most common borders

Of the three potential boundaries, the heliosheath is the one most often used by researchers and NASA to define the solar system. The reason is that it is the easiest to locate and the magnetic characteristics on the two sides are significantly different.

But that doesn't mean everything beyond the heliosheath has to be an interstellar object, like the giant space rock 'Oumuamua, Reisenfeld says. "The Oort cloud is also part of the stuff that makes up planets. So it's solar system material, not interstellar material," he says.

Thu Thao (According to Live Science )

Source link